Chicago: The 110 story high Willis Tower, formerly known as the Sears Tower, is one of the tallest building in the world and the tallest building in America. Sears Roebuck and Co., once the largest retailer in the world, hired architects Skidmore, Owings and Merrill to design what would become one of the largest office buildings in the world. In 2009 U.S. Equities renovated the 103rd floor Skydeck adding "The Ledge", a glass bay that extends out from the building. .Images available in Raw files..Jose More Photography.